Geochemical rock sampling for gold in the Munro Township area, Ontario: an orientation survey

CIM Bulletin, Vol. 82, No. 926, 1989

G.R. Webber, Department of Geological Sciences, McGill University, and P.J. Whittaker*, Ontario Geological Survey

A multielement (Au, Cu, Pb, Zn, Ni, Cr, Ag, As, Hg, Co, and S) geochemical rock sampling survey was carried out in 1977 in the Munro Township area of Ontario to assess the application of rock geochemistry for gold exploration in the region. Detailed sampling with analysis for gold and arsenic was done in 1986 in the immediate vicinity of the Croesus Mine. Samples of quartz veins and rock formations were taken in regional traverses and in more detail near old showings, prospect pits, and trenches. Quartz, graywacke, carbonate rock, and rhyolite contain the highest concentrations of gold for samples taken away from the old workings. Ultramaflc rocks and gab-bro have uniformly low gold. Basalt samples have slightly higher geometric means, but individual samples contain high gold concentrations. Multielement highs are mostly in mineralized quartz samples. Gold distribution is independent of other elements in most other rock types. Samples near old showings possess elevated concentrations of gold indicating that prospecting for individual mineral deposits by bedrock sampling is feasible. Concentrations of gold greater than 100 ppb are mostly within 30 m of old workings. Those samples which contain greater than 1000ppb Au were obtained from quartz veins, basalt, graywacke, and rhyolite. High concentrations of gold were not notably concentrated near the Contact Fault although some anomalous samples came from near and on both sides of the fault. Arsenic concentrations are elevated near the Contact Fault. Detailed sampling near the Croesus Mine suggests that gold was introduced with faulting, alteration and quartz veining. Gold and arsenic have been added to the wall rock in the vicinity of the main veins.  
Mots Clés: Geochemistry, Gold, Exploration, Geology.